So I had dinner at the MIA airport the other night, dinner for two. When the bill came the place automatically added a 15% gratuity. I gave them my credit card, to my surprise when it was time to sign they added an additional line for “tip”. Is this normal?

I felt like forcing me tip what they thought was fair was enough. To be honest, I was going to tip 20% but after seeing that automatically factored in, I left it at that.